1. Field
The following description relates to an integrating analog-digital converter. The following description also relates to an integrating analog-digital converter configured to be resistant to switching noise when converting an analog input signal to a digital output signal and configured to reduce power consumption so as to improve an integrating analog-digital converter.
2. Description of Related Art
An analog-digital converter denotes a device through which an analog physical quantity such as voltage, current, temperature, humidity, pressure, flux, speed, or another physical quantity that takes on a continuous range of values is converted to a digital signal with discrete values. By using such a digital signal, arithmetic is easier, results are more accurate, and the information is easier to process as required. However, as a processing speed of the digital signal increases more and more and a high-resolution digital representation of the analog sign is required, it is helpful for the analog-digital converter, which is one of the core circuits used in this context, to feature a high-resolution.
For example, the analog-digital converter is employed along with a sensor and a computer and other related hardware, or the analog-digital converter is deployed inside a sensor. Here, the sensor is a device that converts the continuous physical quantity to be measured, into a corresponding electrical signal with a corresponding characteristic such as voltage, current or frequency. The analog-digital converter serves to convert the quantity of electricity to a parallel or serial data stream that is readable by a computer. Specifically, the analog-digital converter converts an analog signal to a digital signal at a rapid speed accurately in order to perform real time digital signal processing. The performance of the said analog-digital converter thus determines quality of the sensor or entire system.
With respect to such an analog-digital converter, there are many varieties, such as a coefficient approximation type, a successive approximation type, a flash analog-digital converter (ADC), and an integrator. Among these, an integrating analog-digital converter operates in a manner that integrates a reference voltage that is received along with an analog input voltage under an initial state, until an output of integrator assumes a ground value of zero and operates in a manner that counts the integration time. Therefore, the integrating analog-digital converter operates as a converter device that provides certain characteristics in a sensor apparatus or a measuring apparatus, in regards to realizing a high-resolution, a few offset, and a few gain errors compared with other analog-digital converter.
An integrating analog-digital converter, as shown in FIG. 1, includes an operational amplifier 10 configured to receive a positive reference voltage +VREF or a negative reference voltage −VREF along with an input voltage VIN, whose output is connected to a capacitor C1. The integrating analog-digital converter of FIG. 1 also includes a comparator 20 configured to be connected with the output of the operational amplifier 10. The comparator 20 has the characteristic that an inverting terminal (−) is connected with the output of the operational amplifier 10 and that a non-inverting terminal (+) is grounded.
The integrating analog-digital converter of FIG. 1 is configured such that an operational amplifier 10 receives the positive reference voltage +VREF or the negative reference voltage −VREF together with an input voltage VIN through an inverting terminal (−), by means of a switch SW that operates in accordance with a switch control signal of the integrator logic, under an initial reset state. The input voltage VIN is then charged, during a run-up section, due to using a resistor R1 and a capacitor C1. When the charging is completed, a discharge, during a run-down section, that then takes place according to a switching operation.
Accordingly, the analog value outputs a clock pulse that is compared in the comparator 20. An integral logic unit 30 then counts a clock pulse of a specific frequency that is outputted in the comparator 20 during the time at which the capacitor C1 is discharged. Thus, the comparator 20 outputs a high level when a voltage applied to the inverting terminal (−) of the comparator 20 falls onto the ground level. Thus, a high level value is counted, which is outputted for a specific duration of time in this manner.
However, the aforesaid integrating analog-digital converter presents the following issues.
First, in the integrating analog-digital converter of FIG. 1, a switch SW that operates to provide the positive reference voltage +VREF or the negative reference voltage −VREF to an operational amplifier, is selected in accordance with a level of an input voltage VIN when the capacitor C1 is discharged. As this occurs, due to the switching noise, some situations may take place in which a switch SW does not operate accurately. For example, phenomena may thus take place, where the positive reference voltage +VREF or the negative reference voltage −VREF is not provided to the operational amplifier 10 having a predetermined magnitude. As a result, it thus disadvantageously causes the conversion capabilities of the integrating analog-digital converter to be impaired. Furthermore, in cases where such an integrating analog-digital converter is applied to a sensor, a sensing capability may be generally degraded.
Further, in the integrating analog-digital converter of FIG. 1, there exists a section that simultaneously receives or simultaneously blocks a positive reference voltage +VREF and a negative reference voltage −VREF so as to cope with noise that is generated when a switch SW is involved in a switching operation when integrating. However in this approach, all of the switches assume a turned on state, and relatively more power is thereby consumed.
Additionally, the integrating analog-digital converter of FIG. 1 realizes a resistor-capacitor (R-C) integrator using an operational amplifier 10, such that a bulk capacitor C1 and a resistor R1 are to be used.
Furthermore, in some approaches there exists a residue bit of which an input voltage is not used when converting from analog to digital. Here, the residue bit is a usual ‘1’ bit, and becomes ‘0’ or ‘1’. However, the residue bit is a reason why a resolution is degraded because of the incorporation of unused bits. Some approaches provide a structure of processing the residue bit. Thus, in some approaches, an analog-digital converter containing structure specialized for processing the residue bit is additionally used. This leads to another disadvantage of enlarged circuit size.